Process for production of polyphenylene sulfide resin

ABSTRACT

A process for producing a polyphenylene sulfide resin with properties of (1) 0.3 wt % or less in the amount of the volatile gas generated when heated and melted at 320° C. in vacuum for 2 hours, (2) 0.3 wt % or less in the ash content achieved when incinerated at 550° C., (3) 4.0 wt % or less in the residue amount achieved when a solution with 1 part by weight of the polyphenylene sulfide resin dissolved in 20 parts by weight of 1-chloronaphthalene is pressure-filtered by a PTFE membrane filter with a pore size of 1 μm at 250° C. for 5 minutes, and (4) higher than 500 g/10 min in melt flow rate (according to ASTM D-1238-70: measured at a temperature of 315.5° C. and at a load of 5000 g), by acid-treating a polyphenylene sulfide resin in an acid treatment step and subsequently treating it for thermal oxidation in a thermal oxidation step.

RELATED APPLICATIONS

This is a §371 of International Application No. PCT/JP2007/071699, withan inter-national filing date of Nov. 8, 2007 (WO 2009/060524 A1,published May 14, 2009), the subject matter of which is incorporated byreference.

TECHNICAL FIELD

This disclosure relates to a process for producing a polyphenylenesulfide resin excellent in melt flowability, small in metal content andin the amount of the volatile component generated during melting andexcellent in molding stability and wet heat resistance.

BACKGROUND

Polyphenylene sulfide (hereinafter abbreviated as PPS) resins haveexcellent properties suitable as engineering plastics such as heatresistance, barrier properties, chemicals resistance, electricinsulation and wet heat resistance, and are used as variouselectric/electronic parts, machine parts, automobile parts, films,fibers and the like mainly produced by injection molding and extrusionmolding.

However, PPS resins are high in melt-processing temperature owing totheir high melting points and are likely to generate volatile componentsduring melt processing. Particularly a PPS resin required to haveelectric resistance as used for electric/electronic parts isacid-treated to be lowered in metal content. Such a PPS resin remarkablygenerates a volatile component, to contaminate the mold or to clog themold vent for causing molding failures as the case may be, and thereforeis highly desired to be decreased in volatile component. The volatilecomponent can be decreased by heat-treating the PPS at a temperature oflower than the melting point, but an excessive heat treatment bringsabout such problems as lower moldability owing to an excessive rise ofmelt viscosity and to the production of a gelation product. Our processis based on the finding that, if an acid-treated PPS resin is subjectedto thermal oxidation treatment under specific conditions, the PPS resincan be made smaller in metal content and can be greatly decreased involatile component without highly rising in melt viscosity.

Thermal oxidation treatment of a PPS resin has been performed sincebefore. For example, JP 63-207827 A discloses an extruded articleobtained by curing a PPS resin for keeping the polymer viscosity in arange from 5000 to 16000 poises (500 to 1600 Pa·s) (310° C., shear rate200/sec) and for keeping the non-Newtonian coefficient n in a range from1.5 to 2.1 and subsequently melt-extruding the cured resin. However,5000 poises correspond to a melt flow rate of less than 100 g/10 min,and since the PPS resin is so high in melt viscosity as to considerablylower the flowability at the time of injection molding, the PPS resin isunsuitable for injection molding especially when it is afiller-containing PPS resin composition. Further, the PPS resindisclosed in JP '827 is relatively large in the degree of thermaloxidation treatment, and if the degree of thermal oxidation treatment istoo large, the gas decreasing effect is saturated, and on the otherhand, there is a problem that the melt flowability declines.

JP 6-248078 A discloses a method for treating a granular PPS resin witha weight average molecular weight of 30,000 or higher and an averageparticle size of 50 μm or smaller for thermal oxidation. However, asdescribed in JP '078, for obtaining a PPS resin with a weight averagemolecular weight of 30,000 or higher and an average particle size of 50μm or smaller, a special polymerization reactor or grinding is necessaryto increase the cost, and therefore the method cannot be used as ageneral method. Further, such fine PPS particles cannot be smoothly fedinto an extruder for melt kneading, to decrease the melt-kneaded andextruded amount per unit time uneconomically.

JP 1-121327 A discloses a method for curing a PPS resin in a low oxygenatmosphere, but does not refer to achieving both excellent meltflowability and low volatile component content by performing thermaloxidation treatment under specific conditions.

JP 2002-293934 A discloses a method comprising the steps of recovering aPPS resin by a flush method after polymerization, washing it with hotwater of 130° C. or higher, filtering and treating with an acidicaqueous solution. This method can certainly decrease ionic impuritiesand the volatile component, but since dry PPS is treated at 180° C. for4 hours in a nitrogen stream in the examples described in the document,the effect of decreasing the volatile component is small.

It could therefore be helpful to address the problem of obtaining a PPSresin excellent in melt flowability, small in metal content and in theamount of the volatile component generated during melting, and excellentin molding stability and wet heat resistance.

SUMMARY

We discovered a process for producing a PPS resin remarkably decreasedin the amount of the volatile component generated during melting,excellent in melt flowability and decreased in metal content to beexcellent in molding stability and wet heat resistance, by relativelylightly treating an acid-treated PPS resin with a relatively lowviscosity for thermal oxidation.

We provide:

-   -   1. A process for producing a polyphenylene sulfide resin with        properties of (1) 0.3 wt % or less in the amount of the volatile        gas generated when heated and melted at 320° C. in vacuum for 2        hours, (2) 0.3 wt % or less in the ash content achieved when        incinerated at 550° C., (3) 4.0 wt % or less in the residue        amount achieved when a solution with 1 part by weight of the        polyphenylene sulfide resin dissolved in 20 parts by weight of        1-chloronaphthalene is pressure-filtered by a PTFE membrane        filter with a pore size of 1 μm at 250° C. for 5 minutes,        and (4) higher than 500 g/10 min in melt flow rate (according to        ASTM D-1238-70: measured at a temperature of 315.5° C. and at a        load of 5000 g), by acid-treating a polyphenylene sulfide resin        in an acid treatment step and subsequently treating it for        thermal oxidation in a thermal oxidation step.    -   2. A process for producing a polyphenylene sulfide resin,        according to the abovementioned 1, wherein in the acid treatment        step, the polyphenylene sulfide resin is immersed in an acid or        an aqueous solution of the acid for treatment.    -   3. A process for producing a polyphenylene sulfide resin,        according to the abovementioned 1 or 2, wherein in the acid        treatment step, the polyphenylene sulfide resin is immersed in        an acid or an aqueous solution of the acid for treatment at pH 2        to 8 and at 80 to 200° C.    -   4. A process for producing a PPS resin, according to any one of        the abovementioned 1 through 3, wherein the step of treating the        PPS resin by hot water at 80 to 200° C. is performed before the        step of acid-treating the PPS resin.    -   5. A process for producing a PPS resin, according to any one of        the abovementioned 1 through 4, wherein in the step of treating        the PPS resin for thermal oxidation, the PPS resin is        heat-treated in an atmosphere with an oxygen concentration of 2        vol % or more at 160 to 270° C. for 0.5 to 10 hours.    -   6. A process for producing a PPS resin, according to any one of        the abovementioned 1 through 5, wherein the PPS resin is a resin        recovered by a flush method.

We thus provide a PPS resin remarkably decreased in the amount of thevolatile component generated during melting, excellent in meltflowability and further decreased in metal content to be excellent inmolding stability and wet heat resistance.

DETAILED DESCRIPTION

Selected modes for carrying out our processes are explained below indetail.

The PPS resin obtained by the production process is a polymer having therecurring units, each represented by the following structural formula(I):

In view of heat resistance, it is preferred that the PPS resin contains70% or more of a polymer having the recurring units, each represented bythe abovementioned structural formula. More preferred is 90 mol % ormore. Further, the PPS resin may contain less than about 30% of therecurring units represented by the following structures:

It is desirable that the PPS resin obtained by the production process isrequired to be (1) 0.3 wt % or less in the amount of the volatile gasgenerated when heated and melted at 320° C. in vacuum for 2 hours.Preferred is 0.28 wt % or less, and more preferred is 0.22 wt % or less.It is not preferred that the amount of the gas generated after thermaloxidation treatment is more than 0.3 wt %, since the volatile componentdeposited in the mold and in the old vent portion increases, andtransfer failures and gas yellowing are likely to occur. The lower limitin the amount of the gas generated after thermal oxidation treatment isnot especially limited, but it is uneconomical that the period ofthermal oxidation treatment is long enough to decrease the gasgeneration amount, and further if the period of thermal oxidationtreatment is too long, the gelation product is likely to be produced andmolding failures may be caused.

Meanwhile, the gas generation amount means the amount of the gasvolatilized by heating and melting the PPS resin in vacuum and laterliquefied or solidified by cooling to be deposited. It can be measuredby heating a glass ampoule hermetically containing the PPS resin invacuum in a tubular furnace. The glass ampoule is shaped to have a bellyportion of 100 mm×25 mm, a neck portion of 255 mm×12 mm and a wallthickness of 1 mm. As the particular measuring method, only the bodyportion of the glass ampoule hermetically containing the PPS resin invacuum is inserted into a tubular furnace of 320° C. and heated for 2hours, and the volatile gas is cooled and deposited in the neck portionof the ampoule which is not heated by the tubular furnace. The neckportion is cut out and weighed, and subsequently the deposited gas isdissolved into chloroform, for removal. Then the neck portion is driedand weighed again. From the difference between the weight of the neckportion of the ampoule before removing the gas and that after removingthe gas, the gas generation amount can be obtained.

The PPS resin obtained by the production process is required to be (2)0.3 wt % or less in the ash content achieved when incinerated at 550° C.Preferred is 0.2 wt % or less, and more preferred is 0.1 wt % or less.An ash content of more than 0.3 wt % means that the metal content of thePPS resin is large. A large metal content is not preferred for suchreasons that the electric insulation becomes poor and that the declineof melt flowability and the decline of wet heat resistance can becaused.

The PPS resin obtained by the production process is required to be (3)4.0 wt % or less in the residue amount achieved when a solution with 1part by weight of the PPS resin dissolved in 20 parts by weight of1-chloronaphthalene is pressure-filtered by a PTFE membrane filter witha pore size of 1 μm at 250° C. for 5 minutes. Preferred is 3.5 wt % orless, and more preferred is 3.0 wt % or less. A residue amount of morethan 4.0 wt % means that the thermal oxidation crosslinking of the PPSresin has progressed excessively to increase the gelation product in theresin. It is not preferred that the thermal oxidation crosslinking ofthe PPS resin progresses excessively for such reasons that the effect ofdecreasing the volatile component is small and on the other hand thatthe decline of melt flowability and the production of a gelation productcan cause molding failures. The lower limit of the residue amount is notespecially limited, but is desirably 1.5% or more. Preferred is 1.7% ormore. If the residue amount is smaller than 1.5%, the degree of thermaloxidation crosslinking is too low, and therefore the volatile componentcannot be decreased so much during melting, the volatile componentdecrease effect being likely to remain small.

Meanwhile, the abovementioned residue amount is measured using a sampleobtained by pressing a PPS resin to form a film with a thickness ofabout 80 μm, and using a high temperature filtration device and a SUStest tube equipped with a pneumatic cap and a gathering funnel.Particularly at first a membrane filter with a pore size of 1 μm is setin the SUS test tube, and 1 part by weight of the pressed film with athickness of about 80 μm as a PPS resin and 20 parts by weight of1-chloronaphthalene are weighed and sealed in the SUS test tube. Thetest tube is set in the high temperature filtration device of 250° C.,and heated and shaken for 5 minutes. Then, an air-containing injector isconnected with the pneumatic cap, and the piston of the injector isextruded for pneumatic filtration in the hot state. For particularlydetermining the residue amount, the membrane filter before filtrationand the membrane filter dried at 150° C. for 1 hour after filtration areweighed, and from the difference of the weights, the residue amount isobtained.

The PPS resin obtained by the production process is required to be (4)higher than 500 g/10 min in melt flow rate (according to ASTM D-1238-70:measured at a temperature of 315.5° C. and at a load of 5000 g). It isnot preferred that the melt flow rate is 500 g/10 min or lower, since inthe case where the PPS resin filled with a large amount of a filler isused, the melt flowability of the PPS resin composition becomes so lowas to destabilize the molding. The upper limit of the melt viscosity ofthe PPS resin obtained by the production process is not especiallylimited, but with view to obtaining a resin (composition) with astrength enduring practical use, 1 Pa·s (300° C., shear rate 1000/sec)or more is preferred.

The PPS resin obtained by the production process is required to satisfyall the abovementioned properties (1) through (4).

A PPS resin is subjected to acid treatment and subsequently to thermaloxidation treatment for obtaining a PPS resin with the specificproperties. The PPS resin to be subjected to the acid treatment and thethermal oxidation treatment, respectively, can be a PPS resin obtainedby any method. Therefore, a commercially available PPS resin can also beused, and a PPS resin produced by polymerizing monomers as describedbelow can also be used.

The method for producing a PPS resin to be subjected to the acidtreatment and the thermal oxidation treatment, respectively, isdescribed below. At first, the polyhalogenated aromatic compound,sulfidizing agent, polymerization solvent, molecular weight modifier,polymerization aid and polymerization stabilizer will be explainedbelow.

Polyhalogenated Aromatic Compound

A polyhalogenated aromatic compound refers to a compound having two ormore halogen atoms per one molecule. Examples of the polyhalogenatedaromatic compound include p-dichlorobenzene, m-dichlorobenzene,o-dichlorobenzene, 1,3,5-trichlorobenzene, 1,2,4-trichlorobenzene,1,2,4,5-tetrachlorobenzene, hexachlorobenzene, 2,5-dichlorotoluene,2,5-dichloro-p-xylene, 1,4-dibromobenzene, 1,4-diiodobenzene,1-methoxy-2,5-dichlorobenzene and the like. Preferably p-dichlorobenzenecan be used. Further, a copolymer obtained by combining two or moredifferent polyhalogenated aromatic compounds can also be used, but it ispreferred that a p-dihalogenated aromatic compound is a major component.

The amount of the polyhalogenated aromatic compound used is in a rangefrom 0.9 to 2.0 moles per 1 mole of the sulfidizing agent for obtaininga PPS resin with a viscosity suitably for processing. A preferred rangeis 0.95 to 1.5 moles, and a more preferred range is 1.05 to 1.2 moles.

Sulfidizing Agent

The sulfidizing agent can be an alkali metal sulfide, alkali metalhydrosulfide or hydrogen sulfide.

Examples of the alkali metal sulfide include lithium sulfide, sodiumsulfide, potassium sulfide, rubidium sulfide, cesium sulfide and amixture consisting of two or more of the foregoing, and among them,sodium sulfide can be preferably used. Any of these alkali metalsulfides can be used as a hydrate or aqueous mixture or anhydride.

Examples of the alkali metal hydrosulfide include sodium hydrosulfide,potassium hydrosulfide, lithium hydrosulfide, rubidium hydrosulfide,cesium hydrosulfide and a mixture consisting of two or more of theforegoing, and among them, sodium hydrosulfide can be preferably used.Any of these alkali metal hydrosulfides can be used as a hydrate oraqueous mixture or anhydride.

Further, a sulfidizing agent prepared from an alkali metal hydrosulfideand an alkali metal hydroxide in situ in a reaction system can also beused. Further, the sulfidizing agent prepared from an alkali metalhydrosulfide and an alkali metal hydroxide can also be transferred foruse in a polymerization vessel.

Furthermore, a sulfidizing agent prepared from an alkali metal hydroxidesuch as lithium hydroxide or sodium hydroxide and hydrogen sulfide insitu in a reaction system can also be used. Moreover, the sulfidizingagent prepared from an alkali metal hydroxide such as lithium hydroxideor sodium hydroxide and hydrogen sulfide can also be transferred for usein a polymerization vessel.

In the case where the sulfidizing agent is partially lost due todehydration operation or the like before initiation of polymerizationreaction, the supplied amount of the sulfidizing agent means theremaining amount obtained by subtracting the loss from the actuallysupplied amount.

Meanwhile, an alkali metal hydroxide and/or an alkaline earth metalhydroxide can also be used together with the sulfidizing agent.Preferred examples of the alkali metal hydroxide include sodiumhydroxide, potassium hydroxide, lithium hydroxide, rubidium hydroxide,cesium hydroxide and a mixture consisting of two or more of theforegoing, and preferred examples of the alkaline earth metal hydroxideinclude calcium hydroxide, strontium hydroxide, barium hydroxide and thelike. Among them, sodium hydroxide can be preferably used.

In the case where an alkali metal hydrosulfide is used as thesulfidizing agent, it is especially preferred to use an alkali metalhydroxide simultaneously, and the amount of the alkali metal hydroxideused is in a range from 0.95 to 1.20 moles per 1 mole of the alkalimetal hydrosulfide. A preferred range is 1.00 to 1.15 moles, and a morepreferred range is 1.005 to 1.100 moles.

Polymerization Solvent

It is preferred to use an organic polar solvent as the polymerizationsolvent. Examples of the organic polar solvent include aprotic organicsolvents typified by N-alkylpyrrolidones such as N-methyl-2-pyrrolidoneand N-ethyl-2-pyrrolidone, caprolactams such as N-methyl-ε-caprolactam,1,3-dimethyl-2-imidazolidinone, N,N-dimethylacetamide,N,N-dimethylformamide, hexamethyl phosphoric acid triamide,dimethylsulfone, tetramethylene sulfoxide, mixtures thereof or the like.Any of these solvents can be preferably used since they are high inreaction stability. Among them, especially N-methyl-2-pyrrolidone(hereinafter may be abbreviated as NMP) can be preferably used.

The amount of the organic polar solvent used is selected in a range from2.0 moles to 10 moles per 1 mole of the sulfidizing agent. A preferredrange is 2.25 to 6.0 moles, and a more preferred range is 2.5 to 5.5moles.

Molecular Weight Modifier

For forming the ends of a produced PPS resin or for adjusting thepolymerization reaction or the molecular weight, a monohalogen compound(not necessarily required to be an aromatic compound) can also be usedtogether with the abovementioned polyhalogenated aromatic compound.

Polymerization Aid

Using a polymerization aid for obtaining a PPS resin with a relativelyhigh polymerization degree in a shorter period of time is one ofpreferred modes. In this case, the polymerization aid means a substancethat can act to increase the viscosity of the PPS resin obtained.Examples of the polymerization aid include an organic carboxylate,water, alkali metal chloride, organic sulfonate, sulfuric acid alkalimetal salt, alkaline earth metal oxide, alkali metal phosphate, alkalineearth metal phosphate and the like. Any one of them can be used alone ortwo or more of them can also be used together. Among them, an organiccarboxylate and/or water can be preferably used.

The abovementioned alkali metal carboxylate is a compound represented bygeneral formula R(COOM)_(n) (where R denotes an alkyl group, cycloalkylgroup, aryl group, alkylaryl group or arylalkyl group respectivelyhaving 1 to 20 carbon atoms; M denotes an alkali metal selected fromlithium, sodium, potassium, rubidium and cesium; and n denotes aninteger of 1 to 3). The alkali metal carboxylate can also be used as ahydrate, anhydride or aqueous solution. Particular examples of thealkali metal carboxylate include lithium acetate, sodium acetate,potassium acetate, sodium propionate, lithium valerate, sodium benzoate,sodium phenylacetate, potassium p-toluoylate, mixtures thereof or thelike.

An alkali metal carboxylate can also be formed by adding almost equalchemical equivalents of an organic acid and one or more compoundsselected from the group consisting of alkali metal hydroxides, alkalimetal carbonates and alkali metal bicarbonates to each other forreaction. Among the abovementioned alkali metal carboxylates, a lithiumsalt is highly dissolvable in the reaction system, having a high aideffect but is expensive, and a potassium salt, rubidium salt or cesiumsalt is considered to be insufficiently dissolvable in the reactionsystem. Therefore, sodium acetate inexpensive and moderately dissolvablein the polymerization system can be most preferably used.

The amount of the polymerization aid, if used, is usually in a rangefrom 0.01 mole to 0.7 mole per 1 mole of the supplied alkali metalsulfide. A preferred range for obtaining a higher polymerization degreeis 0.1 to 0.6 mole, and a more preferred range is 0.2 to 0.5 mole.

Using water as a polymerization aid is one of effective means forobtaining a resin composition highly balanced between flowability andhigh toughness. In this case, the added amount is usually in a rangefrom 0.5 mole to 15 moles per 1 mile of the supplied alkali metalsulfide. A preferred range for obtaining a higher polymerization degreeis 0.6 to 10 moles, and a more preferred range is 1 to 5 moles.

The time when the polymerization aid is added is not especiallyspecified, and the polymerization aid can be added at any time duringthe preliminary step described later, at the time of initiating thepolymerization or during the polymerization, and can also be addedpartially multiple times. However, in the case where an alkali metalcarboxylate is used as the polymerization aid, in view of easy addition,it is preferred to add it at a time at the time of initiating thepreliminary step or at the time of initiation the polymerization.Further, in the case where water is used as the polymerization aid,adding during the polymerization reaction after supplying thepolyhalogenated aromatic compound is effective.

Polymerization Stabilizer

A polymerization stabilizer can be used for stabilizing thepolymerization reaction system and for preventing side reactions. Apolymerization stabilizer contributes to the stabilization of thepolymerization reaction system and to the inhibition of unwanted sidereactions. One of the side reactions is the production of thiophenol,and if a polymerization stabilizer is added, the production ofthiophenol can be inhibited. Examples of the polymerization stabilizerinclude such compounds as alkali metal hydroxides, alkali metalcarbonates, alkaline earth metal hydroxides and alkaline earth metalcarbonates. Among them, alkali metal hydroxides such as sodiumhydroxide, potassium hydroxide and lithium hydroxide are preferred. Theabovementioned alkali metal carboxylates also act as polymerizationstabilizers, and therefore are included in the polymerizationstabilizers. Further, in the case where an alkali metal hydrosulfide isused as the sulfidizing agent, as described before, it is especiallypreferred to use an alkali metal hydroxide simultaneously. The alkalimetal hydroxide that is added by an amount excessive for the sulfidizingagent can also act as a polymerization stabilizer.

Any one of these polymerization stabilizers can be used alone or two ormore of them can also be used in combination. The amount of thepolymerization stabilizer is usually in a range from 0.02 to 0.2 moleper 1 mole of the supplied alkali metal sulfide. A preferred range is0.03 to 0.1 mole, and a more preferred range is 0.04 to 0.09 mole. Ifthe amount is too small, the stabilization effect is insufficient, andif the amount is too large on the contrary, an economical disadvantageoccurs while the polymer yield tends to decline.

The time when the polymerization stabilizer is added is not especiallyspecified and can be added at any time during the preliminary stepdescribed later, at the time of initiating the polymerization or duringthe polymerization, and can also be added partially multiple times.However, in view of easy addition, it is preferred to add at a time atthe time of initiating the preliminary step or at the time of initiatingthe polymerization.

The preliminary step, polymerization reaction step and recovery stepwill be particularly explained below in this order.

Preliminary Step

The sulfidizing agent is usually used as a hydrate, and it is preferredto heat a mixture containing an organic polar solvent and thesulfidizing agent before adding the polyhalogenated aromatic compound,for removing the excessive amount of water outside the system.Meanwhile, in the case where water is removed excessively by thisoperation, it is preferred to add water for covering the shortage.

Further, as described above, as the sulfidizing agent, the alkali metalsulfide prepared from an alkali metal hydrosulfide and an alkali metalhydroxide in situ in a reaction system or in a vessel other than apolymerization vessel can also be used. The method is not especiallylimited, but used is a method comprising the steps of adding an alkalimetal hydrosulfide and an alkali metal hydroxide to an organic polarsolvent desirably in an inert gas atmosphere in a temperature range fromroom temperature to 150° C., preferably room temperature to 100° C., andheating at normal pressure or under reduced pressure to at least 150° C.or higher, preferably to a range from 180 to 260° C., for distillingaway water. At this stage, a polymerization aid can also be added.Further, to promote the removal of water by distillation, toluene or thelike can also be added for performing the reaction.

In the polymerization reaction, it is preferred that the amount of waterin the polymerization system is 0.5 to 10.0 moles per 1 mole of thesupplied sulfidizing agent. In this case, the amount of water in thepolymerization system is the amount obtained by subtracting the amountof water removed outside the polymerization system from the amount ofwater supplied into the polymerization system. Further, the suppliedwater can be any of water, aqueous solution, crystal water or the like.

Polymerization Reaction Step

It is preferred that a sulfidizing agent and a polyhalogenated aromaticcompound are made to react with each other in an organic polar solventin a temperature range from 200° C. to lower than 290° C., for producingPPS resin particles.

When the polymerization reaction step is initiated, the sulfidizingagent and the polyhalogenated aromatic compound are added to the organicpolar solvent desirably in an inert gas atmosphere in a temperaturerange from room temperature to 220° C., preferably 100 to 220° C. Atthis stage, a polymerization aid can also be added. The order forsupplying these raw materials is not established and the raw materialscan also be added simultaneously.

The mixture is usually heated to a range from 200° C. to 290° C. Theheating rate is not especially limited, but usually selected in a rangefrom 0.01 to 5° C./min, and a preferred range is 0.1 to 3° C./min.

In general, the mixture is heated finally to a temperature of 250 to290° C., and is made to react usually at the temperature usually for0.25 to 50 hours, preferably 0.5 to 20 hours.

A method of performing the reaction, for example, at 200° C. to 260° C.for a certain period of time in the stage before the final temperatureis reached, and subsequently heating to a range from 270 to 290° C. iseffective for obtaining a higher polymerization degree. In this case,the reaction time at 200° C. to 260° C. is usually selected in a rangefrom 0.25 hour to 20 hours, preferably in a range from 0.25 to 10 hours.

Meanwhile, for obtaining a polymer with a higher polymerization degree,performing the polymerization in multiple stages is effective. Forperforming the polymerization in multiple stages, it is effective thatthe conversion of the polyhalogenated aromatic compound in the systemreaches 40 mol % or higher, preferably 60 mol % at 245° C.

Recovery Step

After completion of polymerization, a solid material is recovered from apolymerization reaction product containing the polymer, solvent and thelike.

The most preferred methods for recovering the PPS resin include methodsof recovering under a quickly cooling condition, and one of the mostpreferred recovering methods is a flush method. In a flush method, thepolymerization reaction product is flushed from the state of hightemperature and high pressure (usually higher than 250° C. and higherthan 8 kg/cm²) into an atmosphere of normal pressure or reducedpressure, for recovering the polymer as particles while recovering thesolvent. The flushing in this method means to spout the polymerizationreaction product from a nozzle. The atmosphere into which thepolymerization reaction product is flushed is particularly, for example,nitrogen or water vapor of normal pressure, and the temperature isusually selected in a range from 150° C. to 250° C.

According to a flush method, the solid material can be recoveredsimultaneously with the recovery of the solvent, and the recovery timecan also be relatively short. Therefore, a flush method is aneconomically excellent recovery method. In the recovery method, an ioniccompound typified by sodium and an organic low polymerization product(oligomer) tend to be incorporated into the polymer in the process ofsolidification.

However, the method for recovering the PPS resin used in the productionprocess is not limited to a flush method. A method of recovering thepolymer particles by slow cooling (quenching method) can also be used ifthe method satisfies the requirements. However, in view of economicefficiency and performance, it is more preferred to use the PPS resinrecovered by a flush method for the production process.

The acid treatment and the thermal oxidation treatment of a PPS resin asessential requirements will be described below in detail.

In the PPS resin production process, it is essential that the PPS resinobtained, for example, by the abovementioned polymerization reactionstep and recovery step is acid-treated in the acid treatment step, andit is preferred that a hot water treatment step is performed before acidtreatment step. Further, a step of washing by an organic solvent mayalso be performed before the acid treatment step and the hot watertreatment step.

The acid used in the acid treatment is not especially limited, if itdoes not act to decompose the PPS resin, and the examples of the acidinclude acetic acid, hydrochloric acid, sulfuric acid, phosphoric acid,silicic acid, carbonic acid, propionic acid and the like. Among them,acetic acid and hydrochloric acid can be more preferably used, but anacid that decomposes or deteriorates the PPS resin, such as nitric acid,is not preferred.

When an aqueous solution of an acid is used, it is preferred that thewater is either distilled water or deionized water. It is preferred thatthe pH of the acid aqueous solution is 1 to 7, and a more preferredrange is 2 to 4. It is not preferred that pH is 7 or larger, since themetal content of the PPS resin increases. It is not preferred eitherthat pH is smaller than 1, since the volatile component of the PPS resinincreases.

As the acid treatment method, it is preferred to immerse the PPS resinin an acid or an aqueous solution of the acid, and as required, stirringand heating can also be performed. When heating is performed, it ispreferred that the temperature is 80 to 250° C. A more preferred rangeis 120 to 200° C., and a further more preferred range is 150 to 200° C.It is not preferred that the temperature is lower than 80° C. for suchreasons that the acid treatment effect is small and that the metalcontent increases, and it is not preferred either in view of safety thatthe temperature is higher than 250° C., since the pressure becomes toohigh. Further, when the PPS resin is immersed in an aqueous solution ofan acid for treatment, it is preferred that the pH achieved by the acidtreatment is lower than 8, and a pH range from 2 to 8 is more preferred.It is not preferred that pH is larger than 8, since the metal content ofthe PPS resin increases.

It is preferred that the acid treatment time for the reaction betweenthe PPS resin and the acid to reach satisfactory equilibrium is 2 to 24hours in the case where the treatment is performed at 80° C., and it ispreferred that the time is 0.01 to 5 hours in the case where thetreatment is performed at 200° C.

As for the ratio between the PPS resin and the acid or the acid aqueoussolution in the acid treatment, since it is preferred to keep the PPSresin sufficiently immersed in the acid or in the acid aqueous solutionduring the treatment, it is preferred to use 0.5 to 500 L of the acid oracid aqueous solution per 500 g of the PPS resin. A more preferred rangeis 1 to 100 L, and a further more preferred range is 2.5 to 20 L. It isnot preferred that the amount of the acid or acid aqueous solution issmaller than 0.5 L per 500 g of the PPS resin, since the PPS resincannot be sufficiently immersed in the aqueous solution, being onlyinsufficiently washed to be larger in metal content. Further, it is notpreferred either that the amount of the acid or acid aqueous solution ismore than 500 L per 500 g of the PPS resin, since the amount of thesolution becomes so large for the amount of the PPS resin that theproduction efficiency declines remarkably.

The acid treatment is performed by a method of supplying a predeterminedamount of the PPS resin into predetermined amounts of water and the acidand heating/stirring in a pressure vessel, or a method of continuouslyperforming the acid treatment or the like. As the method for separatingthe aqueous solution and the PPS resin from the treatment solution aftercompletion of the acid treatment, filtration using a sieve or filter issimple and, for example, natural filtration, pressurized filtration,reduced pressure filtration, centrifugal separation or the like can beused. For removing the acid and impurities remaining on the surface ofthe PPS resin separated from the treatment solution, it is preferred towash with cold or hot water several times. The washing method can be amethod of watering the PPS resin on a filtration device while filtering,or a method of supplying the separated PPS resin into prearranged waterand filtering again, for separating the aqueous solution and the PPSresin. It is preferred that the water used for washing is eitherdistilled water or deionized water.

It is preferred to perform hot water treatment by the following methodbefore the acid treatment step. It is preferred that the water used forthe hot water treatment is either distilled water or deionized water. Itis preferred that the hot water treatment temperature is 80 to 250° C. Amore preferred range is 120 to 200° C., and a further more preferredrange is 150 to 200° C. It is not preferred that the temperature islower than 80° C. for such reasons that the hot water treatment effectis small and that the volatile gas generation amount increases, and itis not preferred either in view of safety that the temperature is higherthan 250° C. since the pressure becomes too high.

It is preferred that the hot water treatment time is long enough toallow the sufficient extraction treatment by the PPS resin and hotwater. A preferred range of the treatment time at 80° C. is 2 to 24hours, and a preferred range of the treatment time at 200° C. is 0.01 to5 hours.

It is preferred that the ratio between the PPS resin and water in thehot water treatment is such as to allow treatment in the state where thePPS resin is sufficiently kept immersed in water. It is preferred thatthe amount of water per 500 g of the PPS resin is 0.5 to 500 L. A morepreferred range is 1 to 100 L, and a further more preferred range is 2.5to 20 L. It is not preferred that the amount of water is smaller than0.5 L per 500 g of the PPS resin for such reasons that the PPS resincannot be sufficiently kept immersed in water, being only insufficientlywashed and that the volatile gas generation amount increases. Further,it is not preferred either that the amount of water is more than 500 Lper 500 g of the PPS resin, since the amount of water becomes so largefor the amount of the PPS resin that the production efficiency declinesremarkably.

The operation of the hot water treatment is not especially limited, anda method of supplying a predetermined amount of the PPS resin into apredetermined amount of water and heating/stirring in a pressure vessel,or a method of continuously performing the hot water treatment or thelike can be used. The method of separating the aqueous solution and thePPS resin from the treatment solution after completion of the hot watertreatment is not especially limited, but filtration using a sieve or afilter is simple and, for example, natural filtration, pressurizedfiltration, reduced pressure filtration, centrifugal filtration or thelike can be used. For removing the impurities remaining on the surfaceof the PPS resin separated from the treatment solution, it is preferredto wash with cold or hot water several times. The washing method is notespecially limited, and can be a method of watering the PPS resin on afiltration device while filtering, or a method of supplying theseparated PPS resin into prearranged water and filtering again, forseparating the aqueous solution and the PPS resin. It is preferred thatthe water used for washing is either distilled water or deionized water.

Further, since the decomposition of PPS end groups during the acidtreatment and during the hot water treatment is not preferred, it isdesirable to perform the acid treatment and the hot water treatment inan inert atmosphere. The inert atmosphere can be nitrogen, helium, argonor the like, but a nitrogen atmosphere is preferred from an economicalviewpoint.

Before the acid treatment step and the hot water treatment step, a stepof washing with an organic solvent can also be used. The method is asdescribed below. The organic solvent used for washing the PPS resin isnot especially limited if it does not act to decompose the PPS resin.Examples of the organic solvent include nitrogen-containing polarsolvents such as N-methyl-2-pyrrolidone, dimethylformamide,dimethylacetamide, 1,3-dimethylimidazolidinone, hexamethyl phosphorusamide and piperazinones, sulfoxide/sulfone-based solvents such asdimethyl sulfoxide, dimethylsulfone and sulfolane, ketone-based solventssuch as acetone, methyl ethyl ketone, diethyl ketone and acetophenone,ether-based solvents such as dimethyl ether, dipropyl ether, dioxane andtetrahydrofuran, halogen-based solvents such as chloroform, methylenechloride, trichloroethylene, ethylene dichloride, perchloroethylene,monochloroethane, dichloroethane, tetrachloroethane, perchloroethane andchlorobenzene, alcohol/phenol-based solvents such as methanol, ethanol,propanol, butanol, pentanol, ethylene glycol, propylene glycol, phenol,cresol, polyethylene glycol and polypropylene glycol, aromatichydrocarbon-based solvents such as benzene, toluene, xylene and thelike. Among these organic solvents, it is especially preferred to useN-methyl-2-pyrrolidone, acetone, dimethylformamide, chloroform or thelike. Any one of these organic solvents can be used alone or two or moreof them can also be used as a mixture.

The method for washing with an organic solvent can be, for example, amethod of immersing the PPS resin into the organic solvent, and asrequired, stirring or heating can also be performed. The washingtemperature for washing the PPS resin with the organic solvent is notespecially limited and an arbitrary temperature can be selected in arange from room temperature to about 300° C. If the washing temperatureis higher, the washing efficiency tends to be higher, and usually asufficient effect can be obtained at a washing temperature of roomtemperature to 150° C. The washing can also be performed in a pressurevessel under pressurization at a temperature higher than the boilingpoint of the organic solvent. Further, the washing time is notespecially limited either. In the case of batch washing, thoughdepending on the washing conditions, usually a sufficient effect can beobtained by washing for 5 minutes or more. Continuous washing can alsobe performed.

The acid treatment, the hot water treatment and the washing with anorganic solvent can also be appropriately combined.

We found that only if a PPS resin is acid-treated before it is subjectedto the thermal oxidation treatment, a PPS resin excellent in meltflowability, small in metal content and in the amount of the volatilecomponent generated during melting and excellent in molding stabilityand wet heat resistance can be obtained. Unless the PPS resin isacid-treated before it is subjected to the thermal oxidation treatment,both excellent melt flowability and the inhibition of the volatilecomponent during melting cannot be achieved, and as a result, a PPSresin excellent in moldability and wet heat resistance cannot beobtained.

In the PPS resin production process, the abovementioned acid treatmentand hot water treatment or washing with an organic solvent are followedby the thermal oxidation treatment. The thermal oxidation treatmentrefers to the treatment performed by heating the PPS resin in an oxygenatmosphere or by adding a peroxide such as H₂O₂ or a sulfurizing agentsuch as S to the PPS resin and subsequently heating, and in view oftreatment simplicity, heating in an oxygen atmosphere is especiallypreferred.

The heater used for the thermal oxidation treatment can be an ordinaryhot air dryer, rotary heater or heater with stirring blades, but in thecase where an efficient and homogeneous treatment is intended, it ismore preferred to use a rotary heater or heater with stirring blades. Itis desirable that the oxygen concentration in the atmosphere of thethermal oxidation treatment is 2 vol % or higher. More desirable is 8vol % or higher. The upper limit of the oxygen concentration is notespecially limited, but in view of safe operation, about 50 vol % is thelimit, and more preferred is 25 vol % or lower. It is preferred that thethermal oxidation treatment temperature is 160 to 270° C. A morepreferred range is 160 to 220° C. It is not preferred that the thermaloxidation treatment is performed at a temperature higher than 270° C.for such reasons that the thermal oxidation treatment progresses sorapidly as to make the control difficult and that flowability remarkablydeclines. On the other hand, it is not preferred either that thetemperature is lower than 160° C. for such reasons that the thermaloxidation treatment progresses very slowly and that the generated amountof the volatile component increases. It is preferred that the treatmenttime is 0.2 to 50 hours. A more preferred range is 0.5 to 10 hours, anda further more preferred range is 1 to 5 hours. It is not preferred thatthe treatment time is shorter than 0.2 hour for such reasons that thethermal oxidation treatment cannot be performed sufficiently and thatthe amount of the volatile component is too large. It is not preferredeither that the treatment time is longer than 50 hours for such reasonsthat the crosslinking reaction by the thermal oxidation treatmentprogresses to lower the flowability and that the residue amount achievedwhen a solution with 1 part by weight of the PPS resin dissolved in 20parts by weight of 1-chloronaphthalene is pressure-filtered by a PTFEmembrane filter with a pore size of 1 μm at 250° C. for 5 minutesincreases to lower the molding stability.

Further, dry heat treatment can also be performed before and after thethermal oxidation treatment, for the purposes of inhibiting the thermaloxidation crosslinking and removing water. It is preferred that thetemperature is 100 to 270° C., and a more preferred range is 120 to 200°C. Further, it is desirable that the oxygen concentration in this caseis lower than 2 vol %. It is preferred that the treatment time is 0.2 to50 hours. A more preferred range is 0.5 to 10 hours, and a further morepreferred range is 1 to 5 hours. The heat treatment device can be anordinary hot air dryer or rotary heater or heater with stirring blades,but in the case where an efficient and more homogeneous treatment isintended, it is more preferred to use a rotary heater or heater withstirring blades.

The PPS resin obtained by the production process as described above isexcellent in heat resistance, chemicals resistance, flame retardancy,electric properties and mechanical properties and can be applied asinjection molded articles, films, sheets, fibers and the like, beingable to be especially suitably applied for injection molding.

Meanwhile, it is most preferred to obtain a molded article by using onlythe PPS resin obtained by the production process, but as required, it ispermitted to blend a PPS resin not in conformity with the abovementionedconditions. As the blending rate, the PPS resin obtained by theproduction process can be blended by 75 to 25% (for example, 75%, 50%,25%) selected as required.

Further, another resin can also be added to the PPS resin obtained bythe production process to such an effect that the effects are notimpaired. For example, if a small amount of a highly soft thermoplasticresin is added, flexibility and impact resistance can be furtherenhanced. However, it is not preferred that the amount of thethermoplastic resin exceeds 50 wt % of the entire composition, since thefeatures peculiar to the PPS resin will be impaired. Especially adding30 wt % or less is preferred. Examples of the thermoplastic resininclude epoxy group-containing olefin-based copolymers, otherolefin-based resins, polyamide resins, polybutylene terephthalateresins, polyethylene terephthalate resins, polyphenylene ether resins,polysulfone resins, polyallylsulfone resins, polyketone resins,polyetherimide resins, polyarylate resins, liquid crystal polymers,polyether sulfone resins, polyether ketone resins, polythioether ketoneresins, polyetherether ketone resins, polyimide resins, polyamideimideresins, polyethylene tetrafluoride resins and the like.

Further, for the purpose of modification, any of the following compoundscan be added: ordinary additives, for example, coupling agents such asisocyanate-based compounds, organic silane-based compounds, organictitanate-based compounds, organic borane-based compounds and epoxycompounds, plasticizers such as polyalkylene oxide oligomer-basedcompounds, thioether-based compounds, ester-based compounds and organicphosphorus-based compounds, crystal nucleating agents such as talc,kaolin, organic phosphorus compounds and polyethyether ketones, metallicsoaps such as montanic acid waxes, lithium stearate and aluminumstearate, releasing agents such as ethylenediamine-stearic acid-sebacicacid polycondensation product and silicone-based compounds, colorationpreventives such as hypophosphites, further lubricants, ultravioletlight protective agents, colorants, foaming agents and the like. It isnot preferred that the amount of any of the abovementioned compoundsexceeds 20 wt % of the entire composition, since the properties peculiarto the PPS resin will be impaired. Adding 10 wt % or less, preferably 1wt % or less is desirable.

Further, for the purpose of enhancing the mechanical strength, toughnessand the like, an alkoxysilane having at least one type of functionalgroups selected from epoxy groups, amino groups, isocyanate groups,hydroxyl groups, mercapto groups and ureido groups can also be added tothe PPS resin obtained by the production process. Examples of thecompound include epoxy group-containing alkoxysilane compounds such asγ-glycidoxypropyltrimethoxysilane, γ-glycidoxypropyltriethoxysilane andβ-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, mercapto group-containingalkoxysilane compounds such as γ-mercaptopropyltrimethoxysilane andγ-mercaptopropyltriethoxysilane, ureido group-containing alkoxysilanecompounds such as γ-ureidopropyltriethoxysilane,γ-ureidopropyltrimethoxysilane andγ-(2-ureidoethyl)aminopropyltrimethoxysilane, isocyanatogroup-containing alkoxysilane compounds such asγ-isocyanatopropyltriethoxysilane, γ-isocyanatopropyltrimethoxysilane,γ-isocyanatopropylmethyldimethoxysilane,γ-isocyanatopropylmethyldiethoxysilane,γ-isocyanatopropylethyldimethoxysilane,γ-isocyanatopropylethyldiethoxysilane andγ-isocyanatopropyltrichlorosilane, amino group-containing alkoxysilanecompounds such as γ-(2-aminoethyl)aminopropylmethyldimethoxysilane,γ-(2-aminoethyl)aminopropyltrimethoxysilane andγ-aminopropyltrimethoxysilane, hydroxyl group-containing alkoxysilanecompounds such as γ-hydroxypropyltrimethoxysilane andγ-hydroxypropyltriethoxysilane and the like.

The suitably added amount of the silane compound is selected in a rangefrom 0.05 to 5 parts by weight per 100 parts by weight of the PPS resin.

A filler can also be mixed with the PPS resin obtained by the productionprocess to such an extent that the effects are not impaired. Examples ofthe filler include fibrous fillers such as glass fibers, carbon fibers,basalt fibers, potassium titanate whiskers, zinc oxide whiskers, calciumcarbonate whiskers, wollastonite whiskers, aluminum borate whiskers,aramid fibers, alumina fibers, silicon carbide fibers, ceramic fibers,asbestos fibers, gypsum fibers and metallic fibers, silicates such astalc, wollastonite, zeolite, sericite, mica, kaolin, clay, pyrophyllite,bentonite, asbestos and alumina silicate, metal compounds such assilicon oxide, magnesium oxide, alumina, zirconium oxide, titanium oxideand iron oxide, carbonates such as calcium carbonate, magnesiumcarbonate and dolomite, sulfates such as calcium sulfate and bariumsulfate, hydroxides such as calcium hydroxide, magnesium hydroxide andaluminum hydroxide, non-fibrous fillers such as glass beads, glassflakes, glass powder, ceramic beads, carbon nanotubes, fullerenes, boronnitride, silicon carbide, carbon black, silica and graphite. The fillercan also be hollow, and two or more types of these fillers can also beused together. Further, any of these fillers can also be treatedpreliminarily with a coupling agent such as an isocyanate-basedcompound, organic silane-based compound, organic titanate-basedcompound, organic borane-based compound or epoxy compound.

It is preferred that the mixed amount of any of these inorganic fillersis usually 0.0001 to 500 parts by weight per 100 parts by weight of thePPS resin. A more preferred range is 0.001 to 400 parts by weight. Theinorganic filler content can be changed as appropriate for respectiveapplications in view of the balance among strength, stiffness and otherproperties.

Usually typically the PPS resin is supplied into a publicly known meltkneader such as a single-screw extruder, twin-screw extruder, Banburymixer, kneader or mixing roll mill and kneaded with the melt peaktemperature of the PPS resin+5 to 60° C. as the processing temperature.In the case where subsidiary raw materials are used, the mixing order ofraw materials is not especially limited, and usable is any method suchas a method comprising the steps of mixing all the raw materials andmelt-kneading the mixture by the abovementioned kneading method, amethod comprising the steps of mixing some of the raw materials,melt-kneading the mixture by the abovementioned kneading method, andfurther mixing the other raw materials for subsequent melt-kneading, ora method of mixing some of the raw materials, and melt-kneading themixture using a single-screw or twin-screw extruder, while mixing theother raw materials using the side feeder. Moreover, the ingredients tobe added by small amounts can of course be added after the otheringredients are kneaded by the abovementioned method and pelletized, sothat the entire composition thus obtained can be molded.

The PPS resin (composition) obtained as described above is suitableespecially for injection molding. Particular applications of the PPSresin include, for example, electric/electronic parts such as sensors,LED lamps, connectors, sockets, resistors, relay cases, switches, coilbobbins, capacitors, variable capacitor cases, optical pickups,vibrators, various terminal boards, transformers, plugs, printed circuitboards, tuners, speakers, microphones, headphones, small motors,magnetic head bases, power modules, encapsulated semiconductor parts,liquid crystal display parts, FDD carriages, FDD chassis, motor brushholders, parabolic antennas and computer-related parts; household andoffice electric appliance parts such as VTR parts, television parts,irons, hair dryers, rice cooker parts, electronic oven parts, audioapparatus parts including audio parts, audio laser discs and compactdiscs, illumination parts, refrigerator parts, air conditioner parts,typewriter parts and word processor parts; machine-related parts such asoffice computer-related parts, telephone-related parts,facsimile-related parts, copier-related parts, washing fixtures, motorparts, lighters and typewriters; optical devices and precisionmachine-related parts such as microscopes, binoculars, cameras andtimepieces; water service parts such as tap plugs, water mixing faucets,pump parts, pipe joints, water quantity control valves, relief valves,water temperature sensors, water quantity sensors and water line meterhousings; automobile/vehicle-related parts such as valve alternatorterminals, alternator connectors, IC regulators, potentiometer bases forlight dimmers, various valves including exhaust gas valves, variouspipes for fuel and suction and discharge systems, air intake nozzlesnorkels, intake manifolds, fuel pumps, engine cooling water joints,carburetor main bodies, carburetor spacers, exhaust gas sensors, coolingwater sensors, oil temperature sensors, throttle position sensors,crankshaft position sensors, air flow meters, brake pad wear sensors,air conditioner thermostat bases, room hot air flow control valves,radiator motor brush holders, water pump impellers, turbine vanes, wipermotor-related parts, distributors, starter switches, starter relays,transmission wire harnesses, window washer nozzles, air conditionerpanel switch boards, fuel-related electromagnetic valve coils, fuseconnectors, horn terminals, electric equipment part insulation boards,step motor rotors, lamp sockets, lamp reflectors, lamp housings, brakepistons, solenoid bobbins, engine oil filters, ignition device cases,car speed sensors, cable liners, engine control unit cases, enginedriver unit cases, capacitor cases, motor insulation materials andhybrid car control system parts, and other various applications.

EXAMPLES

Our processes are explained below more particularly in reference toexamples, but is not limited thereto or thereby.

In the following examples, material properties were evaluated by thefollowing methods.

Gas Generation Amount

Three grams of a PPS resin was weighed and placed in a glass ampoulehaving a belly portion of 100 mm×25 mm, a neck portion of 255 mm×12 mmand a wall thickness of 1 mm, and the ampoule was sealed in vacuum. Thebody portion only of the glass ampoule was inserted into ceramicelectric tubular furnace ARF-30K produced by K.K. Asahi Rika Seisakushoand heated at 320° C. for 2 hours. The ampoule was taken out, and theneck portion of the ampoule, which was not heated by the tubular furnaceand had a volatile gas deposited therein was cut out using a file andweighed. Subsequently, the deposited gas was dissolved by 5 g ofchloroform and removed, and the neck portion was dried by a glass dryerof 60° C. for 1 hour and weighed again. The difference between theweight of the neck portion of the ampoule before gas removal and thatafter gas removal was calculated as the gas generation amount (wt %).

Ash Content

Accurately weighed 5 g of a sample was placed in a crucible baked at550° C. beforehand, and the crucible was placed in an electric furnaceof 550° C. for 24 hours, for incinerating the sample. The amount of theash remaining in the crucible was accurately weighed, and the rate ofthe measured weight to the weight of the sample not yet incinerated wascalculated as the ash content (wt %).

Residue Amount

A PTFE membrane filter with a pore size of 1 μm weighed beforehand wasset in a SUS test tube equipped with a pneumatic cap and a gatheringfunnel produced by Senshu Scientific Co., Ltd., and 100 mg of a PPSresin pressed to form a film with a thickness of about 80 μm and 2 g of1-chloronaphthalene were placed in the test tube, followed by sealing.The SUS test tube was inserted into high temperature filtration deviceSSC-9300 produced by Senshu Scientific Co., Ltd., and the filtrationdevice was heated and shaken at 250° C. for 5 minutes, to dissolve thePPS resin into 1-chloronaphthalene. A 20 mL injector containing air wasconnected with the pneumatic cap, and the piston was extruded to filterthe solution by the membrane filter. The membrane filter was taken outand dried in vacuum at 150° C. for 1 hour, subsequently being weighed.The difference between the weight of the membrane filter beforefiltration and that after filtration was calculated as the residueamount (wt %).

Melt Flow Rate (MFR)

MFR was measured according to the method specified in ASTM-D1238-70 at atemperature of 315.5° C. and at a load of 5000 g. However, a resin witha low viscosity of more than 1000 g/10 min as MFR is too high inflowability to allow measurement by this measuring method. For the PPSresins low in melt viscosity, the following capillograph was used formeasuring the melt viscosity. When the melt viscosity of a PPS resinwith an MFR of 500 g/10 min was measured, it was found to be about 80Pa·s (300° C., shear rate 1000/sec). This indicates that if PPS resinsnot greatly different in crosslinking degree and not greatly differentin the dependence of melt viscosity on shear rate and temperature havemelt viscosity values of lower than 80 Pa·s, they have MFR values ofhigher than 500 g/10 min.

Melt Viscosity

Capillograph 1C produced by Toyo Seiki Seisaku-Sho, Ltd. was used tomeasure the melt viscosity at 300° C. using a die with an orifice lengthof 10.00 mm and an orifice diameter of 0.50 mm.

Measurement of Cooling Crystallization Temperature (Tmc)

DSC7 produced by Perkin Elmer was used at a heating/cooling rate of 20°C./min in a nitrogen atmosphere using about 10 mg of a sample asfollows:

-   -   (1) Heating from 50° C. to 340° C. and holding at 340° C. for 1        minute    -   (2) Cooling to 100° C.    -   (3) Heating to 340° C. again and holding at 340° C. for 1 minute    -   (4) Cooling to 100° C. again        The cooling crystallization peak temperature appearing in (4)        was employed as the cooling crystallization temperature (Tmc).

Molding Stability

One hundred parts by weight of a PPS resin and 67 parts by weight ofglass fibers (ECS03TN-103/P produced by Nippon Electric Glass Co., Ltd.)were dry-blended, and TEX30α twin-screw extruder (L/D=45.4) produced byThe Japan Steel Works, Ltd. was used for melt-kneading the mixture at ascrew speed of 300 rpm by setting the temperature to keep thetemperature of the resin delivered from the cylinder at 320° C., and thekneaded resin strand was pelletized by a strand cutter. The pellets weredried at 120° C. overnight and supplied into Fanuc Roboshot α-30iinjection molding machine (produced by Fanuc Ltd.), to continuously moldbars (width 12.7 mm, thickness 0.5 mm, side gate 0.5 mm×5.0 mm) underconditions of injection speed 300 mm/sec, injection pressure 40 MPa,cylinder temperature 300° C., mold temperature 150° C., injection time 1second, cooling time 20 seconds, screw speed 100 rpm, back pressure 1MPa and suck-back 10 mm, and the lengths of the molded bars weremeasured as the bar flow lengths. After the first 20 shots were thrownaway, the difference between the maximum bar flow length and the minimumbar flow length in 100 shots was obtained. A case where the differencebetween the maximum bar flow length and the minimum bar flow lengthaccounted for 5% or less of the mean bar flow length of 100 shorts wasevaluated to be “excellent (A),” a case where the difference accountedfor 5% to 10%, “good (B),” and a case where the difference accounted formore than 10%, “poor (C).”

Wet Heat Resistance

One hundred parts by weight of a PPS resin and 67 parts by weight ofglass fibers (ECS03TN-103/P produced by Nippon Electric Glass Co., Ltd.)were dry-blended, and TEX30α twin-screw extruder (L/D=45.4) produced byThe Japan Steel Works, Ltd. was used for melt-kneading the mixture at ascrew speed of 300 rpm by setting the temperature to keep thetemperature of the resin delivered from the cylinder at 320° C., and thekneaded resin strand was pelletized by a strand cutter. The pellets weredried at 120° C. overnight and molded to prepare specimens of 80 mm×80mm×2.0 mm thick using injection molding machine UH1000 (produced byNissei Plastic Industrial Co., Ltd.) at a resin temperature of 300° C.and a mold temperature of 150° C. On an obtained specimen, a coppersheet of 20 mm×20 mm×0.5 mm thick was placed, and they were set in athermo-hygrostat with a temperature of 60° C. and a humidity of 90%, forwet heat treatment for 10 days (240 hours). After completion oftreatment, the copper sheet was visually confirmed. A copper sheet freefrom any change on the surface was evaluated to be “good (B)” and acopper sheet discolored on the surface, “poor (C).”

Reference Example 1 Preparation of PPS-1

An autoclave with a stirrer and a valve at the bottom was charged with8267.4 g (70.0 moles) of 47.5% sodium hydrosulfide, 2925.0 g (70.2moles) of 96% sodium hydroxide, 13860.0 g (140.0 moles) ofN-methyl-2-pyrrolidone (NMP), 1894.2 g (23.1 moles) of sodium acetateand 10500.0 g of ion exchange water, and while nitrogen was fed atnormal pressure, the system was gradually heated to 240° C. taking about3 hours, to distil away 14772.1 g of water and 280.0 g of NMP.Subsequently, the reaction vessel was cooled to 160° C. The amount ofwater remaining in the system per 1 mole of the supplied alkali metalsulfide was 1.08 moles including the water consumed for hydrolysis ofNMP. Further, the scattered amount of hydrogen sulfide was 0.023 moleper 1 mole of the supplied alkali metal sulfide.

Then, 10646.7 g (72.4 moles) of p-dichlorobenzene (p-DCB) and 6444.9 g(65.1 moles) of NMP were added, and the reaction vessel was sealed undernitrogen gas. With stirring at 240 rpm, the system was heated from 200°C. to 270° C. at a rate of 0.6° C./min, and held at 270° C. for 70minutes. The ejection valve at the bottom of the autoclave was opened,and under pressurization by nitrogen, the content was flushed into avessel with a stirrer for 15 minutes and stirred at 250° C. for a whileto remove most of NMP.

The obtained solid and 53 liters of ion exchange water were placed in anautoclave with a stirrer and washed at 70° C. for 30 minutes, andsuction filtration was performed using a glass filter with a pore sizeof 10 to 16 μm. Then, 60 liters of ion exchange water heated to 70° C.was poured into a glass filter with a pore size of 10 to 16 μm, toperform suction filtration for obtaining 18000 g of PPS-1 as a cake(containing 7550 g of the PPS resin).

Reference Example 2 Preparation of PPS-2

Polymerization was performed as described in Reference Example 1, exceptthat sodium acetate was not added at the time of polymerization, toobtain 16800 g of PPS-2 as a cake (containing 7550 g of the PPS resin).

Comparative Example 1

PPS-1 was not subjected any of the hot water treatment, acid treatmentand thermal oxidation treatment.

Comparative Example 2

PPS-1 was subjected to the thermal oxidation treatment without beingsubjected to the hot water treatment and the acid treatment.

The powder of the PPS-1 subjected to the thermal oxidation treatment wasplaced in a heater with a stirrer having a volume of 100 liters andsubjected to the thermal oxidation treatment under the conditions shownin Table 1. Meanwhile, in the thermal oxidation treatment with an oxygenconcentration of 12%, 1.0 liter/min of air and 0.96 liter/min ofnitrogen were introduced into the heater, and an oxygen concentrationmeter was installed in the heater for measuring the oxygenconcentration.

Comparative Examples 3 and 4

PPS-1 was subjected to the acid treatment without being subjected to thehot water treatment, and subsequently was not subjected to the thermaloxidation treatment.

In Comparative Examples 3 and 4, an autoclave with a stirrer was chargedwith 18000 g of PPS-1 as a cake, 40 liters of ion exchange water and 700g of acetic acid (Comparative Example 3) or 43 g of acetic acid(Comparative Example 4), and the atmosphere in the auto-clave wasreplaced by nitrogen. Subsequently, the system was heated to 192° C. andkept at the temperature for 30 minutes to perform the acid treatment.The pH during the acid treatment was as shown in Table 1. The autoclavewas cooled, and the content was filtered by a glass filter with a poresize of 10 to 16 μm. Then, 60 liters of ion exchange water heated to 70°C. was poured into a glass filter, to perform suction filtration forobtaining a cake. The obtained cake was dried in a nitrogen steam at120° C. for 4 hours, to obtain a powder of PPS-1 subjected to the acidtreatment.

Working Examples 1 to 4 and Comparative Examples 5 to 11

PPS-1 was subjected to the acid treatment without being subjected to thehot water treatment.

In Working Examples 1 to 4 and Comparative Examples 5 to 11, anautoclave with a stirrer was charged with 18000 g of PPS-1 as a cake, 40liters of ion exchange water and 700 g of acetic acid (Working Examples1 and 4 and Comparative Examples 5 and 7 to 10) or 43 g of acetic acid(Working Examples 2 and 3 and Comparative Example 6) or 7 g of aceticacid (Comparative Example 11), and the atmosphere in the autoclave wasreplaced by nitrogen. Then, the system was heated to 192° C. (WorkingExamples 1 to 4 and Comparative Examples 5 to 9 and 11) or 70° C.(Comparative Example 10) and kept at the temperature for 30 minutes toperform the acid treatment. The pH during the acid treatment was asshown in Table 1. The autoclave was cooled, and the content was filteredby a glass filter with a pore size of 10 to 16 μm. Subsequently, 60liters of ion exchange water heated to 70° C. was poured into a glassfilter, to perform suction filtration for obtaining a cake. The obtainedcake was dried in a nitrogen stream at 120° C. for 4 hours, to obtain apowder of PPS-1 subjected to the acid treatment.

The powder of PPS-1 subjected to the acid treatment was placed in aheater with a stirrer having a volume of 100 liters, and the thermaloxidation treatment was performed under the conditions shown in Table 1.Meanwhile, in the thermal oxidation treatment with an oxygenconcentration of 12% (Working Examples 1 and 4 and Comparative Examples5 and 7 to 11), 1.0 liter/min of air and 0.96 liter/min of nitrogen wereintroduced into the heater, and an oxygen concentration meter wasinstalled in the heater to measure the oxygen concentration. The thermaloxidation treatment with an oxygen concentration of 21% (WorkingExamples 2 and 3 and Comparative Example 6) was performed in an airatmosphere with air introduced at 1.96 liters/min.

Working Examples 5 to 8 and Comparative Example 13

PPS-1 was subjected to the hot water treatment, subsequently to the acidtreatment and further subsequently to the thermal oxidation treatment.

In Working Examples 5 to 8 and Comparative Example 13, an autoclave witha stirrer was charged with 18000 g of PPS-1 as a cake and 40 liters ofion exchange water, and the atmosphere in the autoclave was replaced bynitrogen. Then, the system was heated to 192° C. and kept at thetemperature for 30 minutes to perform the hot water treatment. Theautoclave was cooled, and the content was suction-filtered by a glassfilter with a pore size of 10 to 16 μm. Subsequently, 60 liters of ionexchange water heated to 70° C. was poured into a glass filter, toperform suction filtration for obtaining a cake. An autoclave with astirrer was charged with the obtained cake, 40 liters of ion exchangewater and 700 g of acetic acid (Working Examples 5, 7 and 8 andComparative Example 13) or 43 g of acetic acid (Working Example 6), andthe atmosphere in the autoclave was replaced by nitrogen. Then, thesystem was heated to 192° C. and kept at the temperature for 30 minutesto perform the acid treatment. The pH during the acid treatment was asshown in Table 1. The autoclave was cooled, and subsequently the contentwas filtered by a glass filter with a pore size of 10 to 16 μm. Then, 60liters of ion exchange water heated to 70° C. was poured into a glassfilter, to perform suction filtration for obtaining a cake. The obtainedcake was dried in a nitrogen stream at 120° C. for 4 hours, to obtain apowder of PPS-1 subjected to the hot water treatment and the acidtreatment. Then, the powder of PPS-1 subjected to the hot watertreatment and the acid treatment was subjected to the thermal oxidationtreatment under the conditions shown in Table 1. In the thermaloxidation treatment with an oxygen concentration of 12% (WorkingExamples 5, 6 and 8) and in the thermal oxidation treatment with anoxygen concentration of 21% (Working Example 7), the air and nitrogenrates were the same as in Working Examples 1 to 4 and ComparativeExamples 5 to 11. The thermal oxidation treatment with an oxygenconcentration of 0% (Comparative Example 13) was performed in a nitrogenatmosphere with nitrogen introduced at 1.96 liters/min.

Comparative Example 12

In Comparative Example 12, the hot water treatment and the thermaloxidation treatment were performed by the same methods as described inWorking Example 5, except that the acid treatment was not performed.

The measured results of the gas generation amount, ash content, residueamount, MFR and Tmc of each PPS resin obtained are shown in Table 1.

As can be seen from Working Examples 1 to 8, if the pH and temperaturefor the acid treatment and the temperature, time and oxygenconcentration for the thermal oxidation treatment are controlled, a PPSresin small in gas generation amount, ash content and residue amount canbe obtained while it can have a melt viscosity in excess of 500 g/10 minas MFR.

Further, the evaluation results of molding stability and wet heatresistance are also shown in Table 1. It can be seen that only when aPPS resin small in gas generation amount, ash content and residue amountand with an MFR of higher than 500 g/10 min is used, molding stabilityand wet heat resistance become good.

On the other hand, in Comparative Example 1, since the acid treatmentwas not performed, the MFR was low and the ash content was large.Further, since the thermal oxidation treatment was not performed, thegas generation amount was large. In Comparative Example 2, since theacid treatment was not performed though the thermal oxidation treatmentwas performed, the MFR was low and the ash content was large. InComparative Examples 3 and 4, since the thermal oxidation treatment wasnot performed though the acid treatment was performed, the gasgeneration amount was large. In Comparative Examples 5 and 6, sincethermal oxidation treatment temperature was too low, the gas generationamount was large. In Comparative Example 7, since the thermal oxidationtreatment time was too short, the gas generation amount was large. InComparative Example 8, since the thermal oxidation treatment time wastoo long, the residue amount was large and the MFR was low. InComparative Example 9, since the thermal oxidation treatment temperaturewas too high, the residue amount was large and the MFR was low. InComparative Example 10, since the acid treatment temperature was woolow, the ash content was large and the MFR was low. In ComparativeExample 11, since the acid treatment effect was not exhibited owing toan alkaline pH, the ash content was large and the MFR was low. InComparative Example 12, since the acid treatment was not performed, theash content was large and the MFR was low. In Comparative Example 13,since the oxygen concentration during the thermal oxidation treatmentwas too low, the impurity removal effect by oxidation was low and thegas generation amount was large.

Since Comparative Examples 1 to 13 have these problems, it can be seenfrom Table 1 that good results could not be obtained in the evaluationof molding stability and wet heat resistance.

TABLE 1 Comparative Example 1 2 3 4 5 6 7 8 9 PPS used PPS-1 PPS-1 PPS-1PPS-1 PPS-1 PPS-1 PPS-1 PPS-1 PPS-1 Hot water treatment Temp. ° C. — — —— — — — — — Acid Treat pH — — 4 7 4 7 4 4 4 treatment Temp. ° C. — — 192192 192 192 192 192 192 Thermal Temp. ° C. — 200 — — 110 150 200 200 280oxidation Time hours — 4 — — 2 2 0.1 60 1 treatment Oxygen concentration% — 12 — — 12 21 12 12 12 Gas generation wt % 0.69 0.26 0.90 0.54 0.850.51 0.80 0.05 0.09 amount¹⁾ Ash content²⁾ wt % 2.58 2.30 0.01 0.14 0.010.14 0.01 0.01 0.01 Residue wt % 2.5 2.6 1.5 1.5 1.5 1.5 1.7 6.2 5.8amount³⁾ MFR⁴⁾ g/10 min 360 330 750 720 740 718 690 210 220 Tmc ° C. 195197 242 220 240 219 239 225 230 Molding stability⁵⁾ C C C C C C C C CWet heat resistance⁶⁾ C C C C C C C C C Comparative Example 10 11 12 13PPS used PPS-1 PPS-1 PPS-1 PPS-1 Hot water treatment Temp. ° C. — — 192192 Acid Treat pH 4 10 — 4 treatment Temp. ° C. 70 192 — 192 ThermalTemp. ° C. 200 200 200 180 oxidation Time hours 2 2 2 4 treatment Oxygenconcentration % 12 12 12 0 Gas generation wt % 0.21 0.20 0.20 0.58amount¹⁾ Ash content²⁾ wt % 1.95 2.10 2.20 0.01 Residue wt % 2.1 2.1 2.01.6 amount³⁾ MFR⁴⁾ g/10 min 320 310 310 60 Tmc ° C. 200 197 197 240Molding stability⁵⁾ C C C C Wet heat resistance⁶⁾ C C C C Sequel ofTable 1 Working Example 1 2 3 4 5 6 7 8 PPS used PPS-1 PPS-1 PPS-1 PPS-1PPS-1 PPS-1 PPS-1 PPS-1 Hot water treatment Temp. ° C. — — — — 192 192192 192 Acid treatment Treat pH 4 7 7 4 4 7 4 4 Temp. ° C. 192 192 192192 192 192 192 192 Thermal oxidation treatment Temp. ° C. 200 200 200240 200 200 180 180 Time hours 2 1 2 1 2 2 4 4 Oxygen concentration % 1221 21 12 12 12 21 12 Gas generation amount¹⁾ wt % 0.28 0.22 0.16 0.200.24 0.20 0.23 0.24 Ash content²⁾ wt % 0.01 0.14 0.14 0.01 0.01 0.140.01 0.01 Residue amount³⁾ wt % 2.1 1.8 1.9 2.2 2.1 2.2 2.4 2.2 MFR⁴⁾g/10 min 580 618 554 510 550 510 540 550 Tmc ° C. 238 215 215 238 237219 237 237 Molding stability⁵⁾ B B B B A A A A Wet heat resistance⁶⁾ BB B B B B B B

Comparative Example 14

PPS-2 was not subjected to any of the hot water treatment, acidtreatment and thermal oxidation treatment.

Comparative Example 15

PPS-2 was subjected to the thermal oxidation treatment without beingsubjected to the hot water treatment and the acid treatment.

In Comparative Example 15, an experiment was performed as described inComparative Example 2, except that PPS-2 was used.

Comparative Examples 16 and 17

PPS-2 was subjected to the acid treatment without being subjected to thehot water treatment, and subsequently was not subjected to the thermaloxidation treatment.

In Comparative Example 16, an experiment was performed as described inComparative Example 3 except that PPS-2 was used. The pH for the acidtreatment was as shown in Table 2.

In Comparative Example 17, an experiment was performed as described inComparative Example 4 except that PPS-2 was used. The pH for the acidtreatment was as shown in Table 2.

Working Examples 9 to 11 and Comparative Example 18

PPS-2 was subjected to the acid treatment without being subjected to thehot water treatment, and subsequently was subjected to the thermaloxidation treatment.

In Working Example 9, an experiment was performed as described inWorking Example 1 except that PPS-2 was used. The pH for the acidtreatment was as shown in Table 2.

In Working Example 10, an experiment was performed as described inWorking Example 2 except that PPS-2 was used and that the thermaloxidation treatment was performed for 6 hours. The pH for the acidtreatment was as shown in Table 2.

In Working Example 11, an experiment was performed as described inWorking Example 4 except that PPS-2 was used. The pH for the acidtreatment was as shown in Table 2.

In Comparative Example 18, an experiment was performed as described inComparative Example 9 except that PPS-2 was used and that 43 g of aceticacid was used for the acid treatment. The pH for the acid treatment wasas shown in Table 2.

Working Examples 12 to 15

PPS-2 was subjected to the hot water treatment, subsequently to the acidtreatment and further subsequently to the thermal oxidation treatment.

In Working Example 12, an experiment was performed as described inWorking Example 5 except that PPS-2 was used. The pH for the acidtreatment was as shown in Table 2.

In Working Example 13, an experiment was performed as described inWorking Example 6 except that PPS-2 was used. The pH for the acidtreatment was as shown in Table 2.

In Working Example 14, an experiment was performed as described inWorking Example 7 except that PPS-2 was used and that the thermaloxidation treatment was performed at 200° C. for 2 hours. The pH for theacid treatment was as shown in Table 2.

In Working Example 15, an experiment was performed as described inWorking Example 8 except that PPS-2 was used. The pH for the acidtreatment was as shown in Table 2.

The measured results of the gas generation amount, ash content, residueamount, MFR and Tmc of each PPS resin obtained are shown in Table 2.

As can be seen from Working Examples 9 to 15 that use PPS-2 lower thanPPS-1 in melt viscosity, since the pH and temperature for the acidtreatment, the temperature, time and oxygen concentration for thethermal oxidation treatment are controlled, the PPS resin obtained issmall in gas generation amount, ash content and residue amount though ithas a melt viscosity in excess of 500 g/10 min as MFR.

Further, the evaluation results of molding stability and wet heatresistance are also shown in Table 2. It can be seen that only when aPPS resin small in gas generation amount, ash content and residue amountand with an MFR of higher than 500 g/10 min is used, molding stabilityand wet heat resistance become good.

On the other hand, in Comparative Example 14, since the acid treatmentwas not performed, the ash content was large, and further since thethermal oxidation treatment was not performed, the gas generation amountwas large. In Comparative Example 15, since the acid treatment was notperformed through the thermal oxidation treatment was performed, the ashcontent was large. In Comparative Examples 16 and 17, since the thermaloxidation treatment was not performed though the acid treatment wasperformed, the gas generation amount was large. In Comparative Example18, since the thermal oxidation treatment temperature was too high, theresidue amount was large and the MFR was low.

Since Comparative Examples 14 to 18 have these problems, it can be seenfrom Table 2 that good results could not be obtained in the evaluationof molding stability and wet heat resistance.

TABLE 2 Comparative Example Working Example 14 15 16 17 18 9 10 11 12 1314 15 PPS used PPS-2 PPS-2 PPS-2 PPS-2 PPS-2 PPS-2 PPS-2 PPS-2 PPS-2PPS-2 PPS-2 PPS-2 Hot water Temp. ° C. — — — — — — — — 192 192 192 192treatment Acid Treat pH — — 4 7 7 4 7 4 4 7 4 4 treatment Temp. ° C. — —192 192 192 192 192 192 192 192 192 192 Thermal Temp. ° C. — 200 — — 280200 200 240 200 200 200 180 oxidation Time hours — 4 — — 1 2 6 1 2 2 2 4treatment Oxygen % — 12 — — 12 12 21 12 12 12 21 12 concentration Gas wt% 0.92 0.29 1.90 0.93 0.10 0.29 0.22 0.22 0.24 0.22 0.23 0.24 generationamount¹⁾ Ash wt % 2.00 1.98 0.05 0.23 0.23 0.05 0.23 0.05 0.05 0.23 0.050.05 content²⁾ Residue wt % 2.0 2.0 1.5 1.5 5.8 2.1 1.9 2.3 2.1 2.2 2.42.2 amount³⁾ MFR⁴⁾ g/10 min >500 >500 >500 >500280 >500 >500 >500 >500 >500 >500 >500 Melt Pa · s 7 12 5 5 >80 11 15 1410 15 12 10 viscosity Tmc ° C. 190 193 238 220 210 233 215 233 234 220234 234 Molding stability⁵⁾ C C C C C B B B A A A A Wet heatresistance⁶⁾ C C C C C B B B B B B B In Tables 1 and 2: ¹⁾Good . . . Gasgeneration amount = or <0.3 wt % Poor . . . Gas generation amount >0.3wt % ²⁾Good . . . Ash content = or <0.3 wt % Poor . . . Ash content >0.3wt % ³⁾Good . . . Residue amount = or <4.0 wt % Poor . . . Residueamount >4.0 wt % ⁴⁾Good . . . MFR >500 g/10 min Poor . . . MFR = or <500g/10 min ⁵⁾Excellent (A) . . . Flowability variation = or <5% Good (B) .. . Flowability variation = 5 to 10% Poor (C) . . . Flowabilityvariation >10% ⁶⁾Good (B) . . . Not changed on the surface of coppersheet Poor (C) . . . Discolored on the surface of copper sheet

INDUSTRIAL APPLICABILITY

A PPS resin excellent in melt flowability, small in metal content and inthe amount of the volatile component generated during melting andexcellent in molding stability and wet heat resistance can be obtained.

1. A process for producing a polyphenylene sulfide resin with propertiesof (1) 0.3 wt % or less in an amount of volatile gas generated whenheated and melted at 320° C. in a vacuum for 2 hours, (2) 0.3 wt % orless in ash content achieved when incinerated at 550° C., (3) 4.0 wt %or less in residue amount achieved when a solution with 1 part by weightof the polyphenylene sulfide resin dissolved in 20 parts by weight of1-chloronaphthalene is pressure-filtered by a PTFE membrane filter witha pore size of 1 μm at 250° C. for 5 minutes, and (4) higher than 500g/10 min in melt flow rate (according to ASTM D-1238-70: measured at atemperature of 315.5° C. and at a load of 5000 g), by acid-treating apolyphenylene sulfide resin in an acid treatment step and subsequentlytreating it for thermal oxidation in a thermal oxidation step.
 2. Theprocess according to claim 1, wherein, in the acid treatment step, thepolyphenylene sulfide resin is immersed in an acid or an aqueoussolution of the acid for treatment.
 3. The process according to claim 1,wherein, in the acid treatment step, the polyphenylene sulfide resin isimmersed in an acid or an aqueous solution of the acid for treatment atpH 2 to 8 and at 80 to 200° C.
 4. The process according to claim 1,wherein the step of treating the polyphenylene sulfide resin by hotwater at 80 to 200° C. is performed before the step of acid-treating thepolyphenylene sulfide resin.
 5. The process according to claim 1,wherein, in the step of treating the polyphenylene sulfide resin forthermal oxidation, the polyphenylene sulfide resin is heat-treated in anatmosphere with an oxygen concentration of 2 vol % or more at 160 to270° C. for 0.5 to 10 hours.
 6. The process according to claim 1,wherein the polyphenylene sulfide resin is a resin recovered by a flushmethod.
 7. The process according to claim 2, wherein, in the acidtreatment step, the polyphenylene sulfide resin is immersed in an acidor an aqueous solution of the acid for treatment at pH 2 to 8 and at 80to 200° C.
 8. The process according to claim 2, wherein the step oftreating the polyphenylene sulfide resin by hot water at 80 to 200° C.is performed before the step of acid-treating the polyphenylene sulfideresin.
 9. The process according to claim 3, wherein the step of treatingthe polyphenylene sulfide resin by hot water at 80 to 200° C. isperformed before the step of acid-treating the polyphenylene sulfideresin.
 10. The process according to claim 2, wherein, in the step oftreating the polyphenylene sulfide resin for thermal oxidation, thepolyphenylene sulfide resin is heat-treated in an atmosphere with anoxygen concentration of 2 vol % or more at 160 to 270° C. for 0.5 to 10hours.
 11. The process according to claim 3, wherein, in the step oftreating the polyphenylene sulfide resin for thermal oxidation, thepolyphenylene sulfide resin is heat-treated in an atmosphere with anoxygen concentration of 2 vol % or more at 160 to 270° C. for 0.5 to 10hours.
 12. The process according to claim 4, wherein, in the step oftreating the polyphenylene sulfide resin for thermal oxidation, thepolyphenylene sulfide resin is heat-treated in an atmosphere with anoxygen concentration of 2 vol % or more at 160 to 270° C. for 0.5 to 10hours.
 13. The process according to claim 2, wherein the polyphenylenesulfide resin is a resin recovered by a flush method.
 14. The processaccording to claim 3, wherein the polyphenylene sulfide resin is a resinrecovered by a flush method.
 15. The process according to claim 4,wherein the polyphenylene sulfide resin is a resin recovered by a flushmethod.
 16. The process according to claim 5, wherein the polyphenylenesulfide resin is a resin recovered by a flush method.